In a large skillet, heat 2 tablespoons extra-virgin olive oil over medium-high heat. Season the scallops with salt and pepper, add to the skillet and cook for 1 minute. Add the asparagus, cherry tomatoes and red onion and cook for 2 minutes. Turn the scallops, then cook until the tomatoes are shriveled and the scallops are cooked through, 2 to 3 minutes. Remove from the heat. Stir in the spinach, then cover and let stand until the spinach is wilted, about 1 minute.