Heat oven to 350°F.

Spray 2-quart microwavable and ovenproof casserole with cooking spray.

In casserole, mix ½ cup pesto, the tomato sauce, tomato paste, pepper flakes and water.

Cover with microwavable plastic wrap.

Microwave on High 3 to 4 minutes or until sauce is hot.

Add pasta; stir gently.

Stir in meatballs and 1 cup cheese.

Push any pasta that sticks up above liquid down into liquid to cover.

Bake 25 minutes.

Meanwhile, in small cup or bowl, mix butter and 2 tablespoons pesto.

Spread mixture on each baguette slice; set aside.

Remove casserole from oven.

Stir pasta; gently fold in cherry tomatoes.

Arrange baguette slices, overlapping if necessary, on pasta mixture to cover most of mixture.

Cover loosely with foil; bake 10 minutes.

Uncover casserole; sprinkle with 2 tablespoons cheese.

Bake about 10 minutes longer or until pasta is fork-tender.