Marinating the Vegetables - To a large mixing bowl, add the yellow, green, orange and red bell peppers.
To the bowl add zucchini, yellow squash, onions, olive oil, balsamic vinegar, salt, pepper, and red pepper flakes.
Mix all of the vegetables together so they’re coated in the oil, vinegar and spices.
Roasting the Vegetables - On a large sheet pan, place the vegetables as flat as possible spreading them out as much as possible.
On top of the vegetables, sprinkle oregano. Bake in a preheated oven, stirring occasionally until the vegetables are lightly browned (about 20 minutes).