On a baking sheet, toss together the broccoli, olive oil, salt, and pepper.
Roast for 15-20 minutes or until the broccoli is slightly charred and cooked to desired tenderness. Broil for 1-2 minutes for an extra char.
While the broccoli is roasting, prepare the rest of the components. Boil the pasta according to the instructions on the package. Reserve about 1 cup of the pasta water. Set aside.
While the pasta is boiling, in a large skillet, heat 1 Tablespoon of olive oil on medium heat. Sauté the garlic and onions for a few minutes, or until the onions are translucent. Set aside.
In a small bowl, whisk together the tahini, pesto, lemon juice, basil, lemon zest, chili flakes, salt, pepper. Set aside.
In the large skillet with the onions and garlic, toss the pasta, sauce, and ½ cup of pasta water. Add more water if needed.
Top with charred broccoli. Garnish with additional lemon zest, basil, and chili flakes if desired.