Cut zucchini into spirals or noodle strands using the vegetable spiralizer or julienne peeler. Set aside noodles.
Heat large pan on medium-high heat. Melt butter/olive oil, then add garlic and shrimp. Cook shrimp until pink and cooked through. Don't let the garlic burn.
Add zucchini noodles and cook until tender, about 3-5 minutes. Zucchini noodles cook really fast, so taste a strand as you cook and decide how firm or "al-dente" you want the zucchini. Don't overcook the zucchini noodles or else they'll become mush.
Remove the pan from the heat, add parmesan cheese, squeeze some lemon juice and season generously with salt and pepper to taste. Add chili flakes then serve warm.