1. Preheat the oven to 400 degrees . Remove peel and pith from grapefruit. Working over a small bowl to collect juice, carve out segments from between membranes; set segments aside. Toss onion with 2 tablespoons grapefruit juice; set aside to soften.
2. Lightly coat a rimmed baking sheet with cooking spray. Pat tofu dry with paper towels, then slice into 1/2-inch cubes; pat cubes dry with more paper towels. Arrange tofu in a single layer on baking sheet and lightly coat with cooking spray; bake until golden and crisp, 12 to 15 minutes. Transfer to a paper towel-lined plate and let cool.
3. In a large bowl, gently toss together tofu, grapefruit segments, grapefruit juice and onion mixture, kale, hazelnuts, oil, salt and pepper until well combined. Top with pecorino Romano.