Preheat oven to 400 degrees. Spray shallow baking sheet with cooking spray.
Place tomato slices on baking sheet; drizzle with olive oil, sprinkle with salt & pepper. Oven roast tomatoes for 10 minutes or until just beginning to bubble.
Divide pepperoni and cheese in two. Layer cheese on bread slices, then top with pepperoni and roasted tomatoes. Close sandwiches.
Melt butter in a non-stick skillet over medium high heat. Pan grill sandwiches for 3-4 minutes per side until golden brown and heated through. Or use your Panini press. Slice in half to serve.