Pre-heat oven at 400°F. Position one rack in the lower third and one in the upper third.
Fill pasta pot with water and a handful of salt. Bring to a boil.
Chop the bell peppers, halve the tomatoes, slice the onion and garlic, and place in a large bowl. Toss with a tablespoon olive oil. Spread them out on a parchment lined baking sheet and place in the oven. Set a timer for 15 minutes.
Cut the asparagus in big chunks, toss them into the same bowl with 1/2 tbsp olive oil, and spread them onto a second baking sheet.
Place defrosted shrimp in the same bowl. Add another 1/2 tbsp of olive oil, a pinch of red pepper flakes and the juice of half a lemon. Toss and spread on the sheet with the asparagus.
After the sheet with bell peppers and tomatoes has been in the oven for 15 minutes, add the second sheet with the shrimp and asparagus. Set a timer for 12 minutes.
Once the shrimp is in the oven, add pasta to the boiling water. If using fresh, set timer for 4 to 6 minutes. If using dry, follow manufacturer's recommendation for al dente pasta. Add frozen peas to the pasta 6 minutes before the end of the pasta's cooking time (or at the same time as the pasta if you are using fresh).
Reserve 1/2 cup of pasta water, drain the rest and place pasta and peas in a serving dish.
The bell peppers and tomatoes should be ready to take out of the oven (about 25 minutes total cooking time). Season them with a pinch of salt and pepper and pour everything on top of the pasta.
Check on the shrimp and asparagus, they should be ready (12 to 15 minutes cooking time). Pour them on top of the pasta and vegetables, along with all the juices from the sheet pan.
Add a big handful of shredded Parmesan (save some for serving), the reserved pasta water, and slivered basil. Toss everything together.
Served topped with the rest of the shredded Parmesan.