Rigatoni with Grilled Peppers and Onions (Onjali Pettingill)

2 medium red onions, sliced into 1/2-inch-thick rings
2 large red bell peppers, cut into quarters
1 tablespoon olive oil Kosher salt and pepper
12 ounces (4 to 5 cups) rigatoni
1 bunch spinach, stems trimmed, or one 5-ounce package
1 cup (about 3 1/2 ounces) grated Parmesan
3/4 cup basil leaves, thinly sliced
Bring a large pot of water to a boil.

Heat a grill or grill pan to medium-high.
In a large bowl, toss the onions, bell peppers, oil, 1/2 teaspoon salt, and 1/2 teaspoon pepper. Grill, turning occasionally, until tender, 8 to 10 minutes. Transfer to a cutting board and cut into bite-size pieces.

Cook the pasta according to the package directions. Reserve 1 cup of the cooking water, drain the pasta, and return the pasta to the pot. Add the grilled vegetables, spinach, the reserved pasta water, and 3/4 cup of the Parmesan to the pasta and toss to combine. Top with the basil and the remaining Parmesan before serving.