can i assemble it the night before and cook it next day?
I wouldn't. And "shrimp scampi" is redundant as it means " shrimp shrimps". But baked sounds all wrong too. If you really want to do them "scamp" style I would stick with the skillet method; hot oil, garlic etc. They cook up really fast so there's hardly a reason to overnight them.
I've made baked scampi - it was pretty good. I did mine with butter. Of course, it was an insanely easy and quick recipe, so I'm not sure if there's much point in prepping the recipe ahead of time. If you just mean can you peel and devein the shrimp, mince the garlic and juice the lemon the night before - yeah, I don't see why not (so long as the shrimp is fresh). But really, it's just throwing the ingredients in a dish and popping it in the oven. They probably take as long to prepare as the oven needs to heat up. Just in case you're interested, here's the recipe I used:
Time: About 30 min
1/3 cup olive oil
1 lemon, zested then half cut into thin slices and other half into wedges
3-4 fresh thyme sprigs, leaves removed
sea or kosher salt and fresh black pepper
spaghetti/pasta, couscous or rice for serving
1 pound fresh shrimp, medium-sized, deveined with tails off
5 cloves garlic, minced
1. Preheat oven to 400 degrees F. In a 9x13 baking pan combine olive
oil, lemon zest and thyme. Season with salt and pepper. Bake in oven
for 12 minutes. Meanwhile cook pasta, couscous or rice.
2. Remove pan from oven, add shrimp, garlic and the thin sliced lemons
(don't squeeze them), toss to coat with oil mixture. Bake for 8-10
more minutes or until shrimp turn pink and start to curl. Serve over
pasta, couscous or rice tossed with extra-virgin olive oil and
fresh-squeezed lemon with additional lemon wedges for serving.
From Fine Cooking
The oven method works well and is quick and easy