Mix ground chicken, chopped fresh cilantro, seasoned dry breadcrumbs, salt, and pepper. Form into 4 (1-inch-thick) patties. Coat grill with cooking spray. Grill patties and halved tomatoes, flesh-side down, over medium-high heat 6 minutes, turning, until burgers are cooked through and tomatoes are charred. Top evenly with Cheddar; let melt. Serve on buns with chopped tomatoes and guacamole.