To Make the Shrimp: In a medium bowl, combine the chili powder, salt, pepper, and lime juice. Add the shrimp and toss until coated. Spray a medium skillet with nonstick spray, and heat over medium heat. Add the shrimp and cook for about 4-5 minutes until the shrimp is pink, or fully cooked through. (If using chicken, cook chicken the exact same way. Cook 5-8 minutes, or until white in the thickest piece, and fully cooked through).
To Make the Zoodles: Use a spiralizer, (or julienne slicer/vegetable peeler) to create noodles from the zucchini. (Note: You may eat the zucchini noodles just as it is, or you may warm it through in the microwave for 60 seconds, or in a large skillet, until it is tender to your liking before adding the sauce.)
To Make the Avocado Sauce: In a food processor or blender, pulse the avocado, yogurt, lime juice, garlic, salt, pepper, and cilantro leaves until smooth. In a large bowl, toss the zoodles with the sauce until they are coated in the sauce.
To Serve: Divide the zoodles among serving plates, and top each plate with shrimp. Top with cilantro if desired!