Preheat the oven to 400 degrees F.
Toss the zucchini, yellow squash and bell peppers with olive oil, salt and pepper on a sheet pan. Spread them out in a single layer.
Heat the olive oil in a saucepan over medium heat. Toast the couscous for a few minutes.
Then pour in the water. Cover, lower the heat and simmer the grains for 10 minutes until they are tender.