2 bell peppers (any color), stemmed, seeded and quartered
1 yellow squash, sliced into 1/4-inch-thick rounds
8 ounces shiitake mushrooms, stemmed
2 cloves garlic, unpeeled
2 to 3 sprigs thyme, rosemary or oregano
3 tablespoons extra-virgin olive oil, plus more for brushing
Kosher salt and freshly ground pepper
1 large red onion, sliced into 1/4-inch-thick rounds
1 10 -ounce package couscous
1/2 cup 2% Greek yogurt
1/4 cup sliced almonds, toasted