Preheat oven to 375°F. Trim off squash ends. Cut remaining squash into 1 1/2-inch rings; scoop out and discard seeds and membranes. Arrange rings on a foil-lined baking sheet coated with cooking spray. Coat rings with cooking spray. Bake at 375°F for 45 minutes or until just tender. Cool slightly. Cut through each ring and open slightly to reach strands; carefully scrape out spaghetti-like squash strands.
Heat butter and oil in a medium skillet over medium-high. Add pepper and garlic; cook 30 seconds, stirring constantly. Add shrimp; sauté 2 minutes or until almost done. Add spinach, tossing until spinach wilts. Add squash strands; sprinkle with salt. Toss gently to combine.