Preheat oven to 350°F. Spray a shallow 2 ½-quart casserole dish with nonstick spray. Set aside.
Brown sausage over medium heat, about 9 minutes. Drain well on paper towels.
Return the skillet to the stovetop over medium heat. Reserve about 2 tablespoons of the green and red bell peppers. Add the onions, green bell peppers, and red bell peppers, and cook until tender, 7 to 8 minutes. Transfer the vegetables to a bowl to cool.
Whisk together eggs, milk, half-and-half, salt, and pepper in a large measuring cup or bowl.
Add 2 cups (8 ounces) of tater tots to the prepared casserole dish. Top with cooked sausage and cooked veggies. Sprinkle with the shredded cheddar and shredded Mozzarella cheeses. Evenly pour the custard over the top of the casserole.
Arrange the remaining frozen tater tots in tight, concentric ovals on top of the cheese. Tuck the reserved raw peppers into the gaps between the tater tots. May be prepared in advance up to this point - cover tightly with aluminum foil and refrigerate overnight.
Bake in a preheated 350°F oven for 55 minutes, adding 10 to 15 minutes if made in advance, until the internal temperature reaches 160°F. Remove from the oven and allow to cool for 5 minutes.
After baking, garnish the bottom curve of the casserole with fresh rosemary sprigs and a "bow" cut from red bell pepper strips.
Yield: 8 servings. (See Tip 7)