Spanakopita Stuffed Shells

Name: Spanakopita Stuffed Shells
Ingredients: 6 ounces jumbo pasta shells (about 22); 5 tablespoons olive oil, divided; 4 medium scallions; 4 cloves garlic; 1/4 cup chopped fresh dill; 1 large lemon; 1 cup shelled fresh or frozen English peas (do not thaw); 5 ounces baby spinach (about 5 cups), or 1/2 (10-ounce) package frozen chopped spinach; 1 1/2 teaspoons kosher salt, divided, plus more for cooking the pasta; 8 ounces whole milk ricotta cheese (1 cup); 4 ounces feta cheese (1 cup crumbled); 2 ounces Parmesan cheese (about 1 cup freshly grated or 1/2 cup store-bought); 1 large egg; 1/4 teaspoon red pepper flakes, plus more for garnish; Freshly ground black pepper; 1/2 cup heavy cream; 2 tablespoons pine nuts (optional)