Vegetarian chili! You could used fresh tomatoes instead of the canned ones, but it would definitely make use of your onions and peppers. Plus you could top it with plenty of yummy cheese and sour cream.

Stuffed peppers?

Roasted tomatoes, onions and peppers tossed with cooked pasta, some salt, pepper, olive oil and, if you like, herbs (thyme works well). Topping with parmesan is optional. Easy and tasty.

italiancaponata or spanish pisto - both amazing options with wonderful recipe variations all over the internet

We just ate really good eastern stuffed cabbage cookedy in tomato sauce with cream cheese topping....you could fill it with lentils or anything really....it was so yummy and you can make many from just one cabbage head.

This recipe has been on my to do list for awhile. It only uses one of the ingredients you listed but I love summertime tomatoes.

http://www.epicurious.com/recipes/food/views/Olive-Oil-Roasted-Tomatoes-and-Fennel-with-White-Beans-360271

Although this is an entirely vegan option, last night I made a vegetable tagine centred around tomatoes, new potatoes, red peppers, onions and leeks, flavoured with cumin, curry powder, green olives and quarters of preserved lemon. (In the past, I've made it with lemon zest and juice when preserved lemons weren't to hand: still very tasty!) It's very easy, it keeps nicely, and it's really delicious.

Oh boy - I made some succotash tacos (or rather, succotash-inspired tacos) last night:

My local market had some fresh chick peas (in the pod... you could use edamame or maybe fresh lima beans), I had an ear of corn in the fridge/cut off kernels, and I picked a couple of red peppers from my garden, added a green onion... sauteed everything for a bit and added some cilantro & lime. Popped it all in a couple of fresh corn tortillas lined with some mexican quesadilla cheese and presto(!) - probably the best dinner I've had in a while. And it was all mine because the hubs and kiddo are scared of green things. :-)

I love the stuffed pepper idea! I've taken the recipe fromThe New Best Recipe Cookbook to potlucks several times and they dissapear FAST! (Use red peppers if you can, it breaks the mental picture of the army-drab colored green peppers a lot of us grew up with AND it tastes better) If you need them to stretch further/smaller portion sizes, cut them inhalf through the stem instead of cutting off a "lid", pepper boats if you will :)

Ratatouille: so amazing. I sautee all my veggies first in olive oil, garlic, and a tiny bit of salt. Layer the following veggies (sliced and sauteed as above), sprinkling grated parmesan between each veggie: eggplant (1), zucchini (2 medium), red onion (1/2 to 1, depending on how much you like), mushrooms (8 oz.), and tomatoe(s) (1 to 2). Top with more parmesan and bake at 400 degrees Farenheit for about forty minutes, or until fork-tender. Make sure you don't sautee your veggies until they're entirely done, otherwise the dish will be overcooked. Also, before anything else, very lightly salt both sides of the eggplant slices and let them sit on paper towels for about ten minutes. Then dab off all the liquid which accumulates. This takes the bitter taste out of the eggplant.

Oh yes! I've also got a lot of peppers, tomatoes and onions from my CSA!

This one is easy peasy and very elegant. Every kind of tomato tart. It uses all the different colors and shapes of tomato from the csa, on a very simple basil custard and a semolina crust (but you could use all regular flour if you want!) I can't stress enough how quick it is to make.

Here's a moroccan spiced chickpea, pepper and tomato stew.

Here's a version of ratatouille in which the eggplant is crispy with a cornmeal crust, and the stewish part has chickpeas and olives.

Here are some ideas from the recipes I have made from our CSA boxes CSA Recipes.

Strongly recommend the pasta with roasted vegetables, yogurt, and balsamic from this very site!

I second the Ratatouille!

Also, if you make the tomato cobbler listed above (and you should, it's AMAZING!), be aware that the recipe makes twice the biscuits you need. Also, you can adjust the proportions of veggies extremely easily. To make them easier, don't roll out your biscuit dough, just do drop biscuits right on the cobbler (makes for fluffier biscuits). For extra protein, dump in some chickpeas!

The gazpacho from Serious Eats! So good.