Shrimp Florentine with Zoodles

Heat 1 tablespoon butter and olive oil together in a large skillet over medium heat; cook and stir zucchini noodles (zoodles), onion, chopped garlic, and 1/2 teaspoon salt until zoodles are tender and onion is translucent, about 5 minutes. Transfer zoodle mixture to a bowl. Heat 2 tablespoons butter in the same skillet; cook and stir shrimp and minced garlic until shrimp are just pink, 3 to 4 minutes. Add spinach, lemon juice, red pepper flakes, 1/2 teaspoon salt, and pepper; cook and stir until spinach begins to wilt, 3 to 4 minutes. Add zoodle mixture; cook and stir until heated through, 2 to 3 minutes.