Bring a large pot of water to a boil, salt generously.
Halve zucchini lengthwise, then slice into 0.5 cm half‑moons. Finely chop garlic. Cut lemon into 4 to 6 wedges depending on the size.
Add spaghetti to boiling water, stir well, and cook for 8 minutes. When draining, reserve half a cup of the pasta water for step 4.
2. Cook zucchini
Heat half a tablespoon of olive oil over medium heat until hot.
Add zucchini and let it sear for a couple of minutes on each side, shaking the pan occasionally.
Transfer to a bowl and set aside until step 3.
Keep the pan over the heat.
3. Cook shrimp
In the same pan — add a few more drops of oil if it looks too dry — place shrimp and cook for a couple of minutes, until opaque and lightly golden.
Add garlic, sun‑dried tomatoes together with the oil from their packet.
Season with salt and pepper.
Return zucchini to pan and cook everything together, stirring carefully, for 3–5 minutes — shrimp will be perfectly done after three, cook a bit longer if you prefer your zucchinis less crunchy.
4. Finish
Return spaghetti to pan along with half of the reserved pasta water and butter.
Gently toss until the sauce coats the pasta, shrimp, and vegetables evenly — add more of the remaining water as needed to achieve a silky consistency.
Squeeze in the juice of lemon (start with one wedge), then toss again and taste. Adjust with more lemon juice, salt, or pepper to your liking.
5. Serve
Divide spaghetti among plates and drizzle with the remaining sauce from the pan.
Serve with the remaining citrus wedges and a sprinkle of grated grana padano.