In a 2- to 3-quart pan, cook rice as directed on package.
Meanwhile, in a 10- to 12-inch frying pan over medium-high heat, stir onions in butter until limp and just beginning to brown, about 4 minutes. Pour into a bowl.
Add broccoli and 1/4 cup water to pan. Bring to a boil over high heat; cover, reduce heat, and simmer until broccoli is barely tender when pierced, about 5 minutes. Drain.
Remove labels from 4 empty food cans (about 2 3/4 in. wide and 4 1/4 in. tall; 14-oz. to 1-lb. size), each with 1 end removed; wash cans with soap, and dry. Rub interiors of cans lightly with oil and set, open end up and slightly apart, in a 10- by 15-inch pan. Spoon 2 tablespoons hot cooked rice into each can and press down with a spoon to compact and make level. Spoon 1/2 cup broccoli onto rice in each can, then 1/4 cup onions and 1 1/2 tablespoons roasted peppers, spreading each level. Continue to layer all ingredients, packing down with a spoon to compact layers as you add each, ending with rice.
Bake in a 375° regular or convection oven until stacks are hot (about 145°) in the center, 20 to 25 minutes. Let rest in cans in pan for 5 minutes. One at a time, invert a dinner plate over each can; hold together and invert can onto plate. With a can opener, cut each can end free; press end down lightly and lift up can to release vegetable-pilaf stack. Lift off can and can end. Garnish plates with cherry tomatoes and parsley. Add salt and pepper to taste.