Lighter Mac and Cheese

Name: Lighter Mac and Cheese
Ingredients: 6 3-inch vine-ripened tomatoes, cut into twenty-four 1/4-inch-thick slices; 3 Tbsp olive oil, divided; 1 1/2 tsp fresh thyme leaves, plus 8 thyme sprigs; Salt and pepper; 5 slices whole wheat bread; 2 Tbsp unsalted butter, divided; 1 lb. elbow macaroni; 2 cups 1% milk, divided; 5 Tbsp all-purpose flour; Pinch nutmeg; 1 tsp cayenne pepper; 1 tsp garlic powder; 2 cups low-sodium chicken broth; 2 1/4 cups (8 oz) grated extra-sharp cheddar cheese; 1/2 cup (1 oz) grated parmesan cheese