How to Make It
Light a grill or preheat a grill pan; oil the grill grate. Brush the tomatoes with olive oil and grill cut side down over high heat until charred, about 4 minutes. Transfer to a plate and let cool completely. Cut the tomatoes into 1/2-inch dice.
In a large bowl, toss the tomatoes with the watermelon, cucumber, lime juice and crushed red pepper. Stir in the cilantro, season with salt and serve at once.