Cook the spaghetti according to the package directions to 'al dente'. Drain well, then toss with the olive oil. Set aside.
1 lb spaghetti, 1 tbsp olive oil
Add the butter to the empty pasta pot, and set over medium low heat. Add the tomatoes & onion, stir. Cook for 5 minutes, stirring often, until the onions are soft. Add the garlic and saute for 30-60 seconds.
1 1/2 cups grape tomatoes, 4 tbsp butter, 1/2 red onion, 1 tsp minced garlic
Add the pasta back to the pot, tossing to combine. Drizzle the dressing overtop, and add the spinach stirring again to evenly combine, and cook for another 5 minutes.
1 cup Greek vinaigrette salad dressing, 6-8 oz fresh baby spinach
Remove the pot from heat and stir in the feta.
6 oz crumbled feta cheese
Serve warm topped with the crumbled feta, and with lemon wedges on the side to squeeze juice over- if desired.
lemon wedges