- Sauté onion in butter and oil until golden, about 5 minutes.
- Stir in pancetta strips; sauté until cooked but not browned, about 5 minutes.
- Stir in tomato and juice, hot pepper, and salt.
- Simmer, uncovered, until liquid reduces and fats pool on surface, about 25 minutes.
- Add more salt to taste, if necessary.
- When sauce is almost done, cook pasta in salted, boiling water according to package directions; drain well.
- While pasta cooks, cut avocados into small dice.
- Toss pasta with sauce, then with avocado and cheese.