Here's a complete, well-balanced meal all on one plate: protein, carbs, greens, and fiber all packed into one dish. This recipe is also great with lean ground turkey instead of beef. Not a broccoli rabe fan? Use regular broccoli instead.
Bring a large pot of water to a boil over high heat. Add 1/8 teaspoon of the salt.
Heat the oil in a large nonstick skillet over medium-high heat. Add the onion and garlic and cook, stirring frequently, until the onion is translucent, about 6 minutes. Add the beef and fennel seed to the skillet. Cook until browned, breaking up the meat with a wooden spoon, about 3-4 minutes.
Stir in the tomatoes, remaining salt, red pepper flakes, and oregano and bring to a boil. Reduce heat to medium-low and simmer until slightly thickened, about 10 minutes.
Meanwhile, add the pasta to the boiling water and cook according to package directions, adding the broccoli rabe to the pasta water 5 minutes before pasta will be done. Cook until the pasta and broccoli rabe are tender. Drain the pasta and broccoli rabe and return to the pot. Add the sauce and toss to combine.