1. Cook pasta according to package directions.
2. Meanwhile, heat oil in Dutch oven over medium-high heat. Add onions and cook until golden, stirring occasionally, 10 minutes. Add spinach, escarole, pepper and salt. Stir briefly. Reduce heat to medium-low; cover and cook 10 minutes more.
3. Drain pasta, reserving 1/4 cup cooking water. Return drained pasta and reserved water to pot; stir in Romano cheese and cooked greens. Transfer to warm serving bowl; serve immediately. Makes 6 main-dish servings.