In a mixing bowl, clean produce or zip-top bag, or with your hands directly on the baking sheet, toss the tomatoes and mushrooms with the oil. You can eyeball this, as you want just enough oil to lightly coat the veggies. Sprinkle with salt and pepper to taste, and then spread in an even layer on the baking sheet. Bake for 15 minutes, give them a stir, and then spread them back out and roast for 5-10 minutes more or until tender and lightly caramelized.