In the meantime, prepare the sauce.
In a small saucepan, whisk together milk, vegetable broth, flour, chili powder, salt, and pepper.
Cook over medium-high heat for 4 to 5 minutes, or until sauce thickens.
Remove from heat.
Drain cooked pasta and return to pot.
Add sauce to the pasta.
Stir in 1 cup shredded mozzarella cheese; stir until melted and well combined.
Layer 1/2-cup tomato sauce on the bottom of the previously prepared baking dish.
Add half of the macaroni mixture over the tomato sauce.
Top with half of the tomato slices; season with salt and pepper.
Sprinkle 1-cup shredded mozzarella cheese.
Dollop on the basil pesto.
Top with the remaining pasta.
Add the rest of the tomato slices; season with salt and pepper.
Sprinkle with the remaining cheese.
Bake for 22 to 25 minutes, or until bubbly and cheese is melted.
Remove from oven.
Let stand 15 minutes.
Cut and serve.