Spicy Skillet Lasagna With Ricotta and Spinach

Name: Spicy Skillet Lasagna With Ricotta and Spinach
Ingredients: ¼ cup extra-virgin olive oil; 1 medium white onion; 6 garlic cloves; 1 tsp. ground cumin; 1 28-oz. can plus 1 15-oz. can crushed San Marzano tomatoes; 3 sprigs basil, leaves picked; 1 Tbsp. crushed red pepper flakes; 1 Tbsp. Diamond Crystal or 1¾ tsp. Morton kosher salt; 8 oz. mature spinach; 1½ tsp. Diamond Crystal or 1 tsp. Morton kosher salt, plus more; 1 lb. lasagna noodles; 2 medium zucchini, thinly sliced about ¼ thick on a mandoline; 2 cups fresh ricotta; ¾ cup whole milk; ½ tsp. freshly ground black pepper; Pinch of ground nutmeg; 4 oz. Parmesan, finely grated, plus more for serving; 1 8-oz. package shredded low-moisture mozzarella; Basil leaves (for serving)