Trim your peppers, cutting off the tops and removing the seeds and white "pith" from the insides as best you can, leaving the pepper whole (except for the tops).
Fill the peppers with your stuffing of choice -- perhaps a mixture of meat, onions, garlic, cooked rice, and spices.
Arrange the filled peppers in a casserole just big though to hold them standing up. (This assumes you cut the tops off -- you can also cut the peppers in half lengthwise, fill them, and then lay them in the casserole dish.)
Make a sauce of canned tomatoes or tomato sauce, more sauteed onions, garlic, S&P, and a little oregano, basil, etc.
Pour the sauce over the peppers.
Cover and bake 1 hour at 350, basting with the sauce now and then, or until the peppers are very tender; uncover and bake another 10 minutes to brown the tops a bit.