Preheat oven to 400 degrees. Place sliced roma tomatoes on a baking sheet. Lightly drizzle with olive oil, and season with garlic powder, salt and pepper. Bake for about 15 minutes or until cooked. Set aside.

Arrange tops and bottoms of the slider buns on a baking sheet. Spread each half with some of the prepared basil pesto, a little goes a long way! 

Stir the balsamic glaze into the leftover shredded beef roast, and re-heat in the microwave until heated through. Evenly distribute the shredded beef onto the bottom slider bun. Place a slice of roasted tomato on the top slider bun. Place a slice of mozzarella on top of the beef. 

Turn the broiler on low, and broil the sliders just until the cheese is melted, and buns being to toast. It will only take a few minutes, watch closely! Remove from oven, place top buns onto bottom buns and serve!