Bell pepper substitute?
 

I love stir-fries and tex mex dishes, but bell peppers (green red and yellow) give me bad indigestion. Onions too but to a lesser degree. Any ideas on what I can substitute in Chinese/mexican style dishes for these veggies? I use french-cut green beans a lot to replace the green bell peppers, wondering what else would give me the nice colors of peppers but without the tummy troubles.

How about carrots?
 

They add a bit of sweetness like red peppers and of course color. Try slicing them into matchstick (or a little bigger) sized strips. Brocolli stalks (save the florettes for something else) cut the same way would add green - just don't over cook them. And tomatoes that have been well deseeded so you have only the flesh. Roma tomatoes work well. Cut them in half, squeeze each half to eliminate the seeds and plup.

Celery, kohlrabi, broccoli, napa, bok choy, cabbage, summer squash & zucchini stir fry up nicely but you have to flash fry the squash (crank up the heat - I cook these last) or they tend to get too limp and soggy.
If you're not watching carbs, black beans & corn are fantastic in Mexican food. I live in New Mexico and they use it quite a bit here, even in salsa. I make my own black beans and cook them up with 2 pieces of chopped turkey bacon (browned before cooking) so it's low fat. Also, there's a popular root veggie called Jimica that ppl seem to like here. It's too carby for me, but they even make coleslaw with it here.
Have you tried using powdered onion? Maybe after it's processed it won't bother your tummy as much...just a thought.