Heat a large skillet over medium heat and add 1 tbsp of olive oil. Add the garlic and scallions and cook, stirring, being careful not to burn the garlic, for 1-2 minutes.
Add the spinach, peas and ¼ tsp salt and cook, stirring, until the peas are tender and spinach is wilted about 3 minutes. Set aside.
Whisk together the eggs, parmesan, basil and ½ tsp salt in a large serving bowl.
Bring a large pot of water to a boil. When the water is boiling, cook pasta according to package instructions. Before draining, reserve 1 cup of the pasta water (we will use it later), then drain the cooked pasta. Toss the cooked pasta with the pea mixture.
Immediately add the hot pasta/veggie mixture to the egg/cheese mixture, tossing quickly (to ensure the eggs do not scramble) until the eggs thicken and create a sauce. Thin the sauce with the reserved pasta water, until it reaches your desired consistency. Add the butter and gently toss to combine. Season with salt and pepper to taste.
Divide the pasta between plates. Top with fresh basil and additional parmesan cheese.