Cook pasta according to package directions. Drain in a colander over a bowl; reserve 1/2 cup pasta water.
Combine ricotta, 1 teaspoon rind, 1/4 teaspoon salt, and black pepper.
Heat 1 tablespoon oil in a large skillet over medium-high heat. Add bell pepper; sauté 2 minutes. Add walnuts, 1/2 teaspoon salt, and garlic; sauté 2 minutes. Stir in 1 tablespoon oil and juice. Add pasta, pasta water, and spinach; cook 1 minute or until spinach wilts. Top with ricotta mixture and rind strips, if desired.