Meanwhile, mix ricotta, 1 tablespoon of lemon zest, salt and pepper, in a small bowl. Set aside.
Chop peppers into bite-sized pieces, mince garlic.
Heat a large skillet over medium-high heat; add 1 tablespoon of oil and allow it to heat up. Add peppers and garlic, cook for 1-2 minutes. Add pasta and chopped walnuts, toss to coat; add spinach and cook for 1-2 minutes so leaves begin to wilt.
Remove from heat, gently fold in ricotta mixture; spritz with fresh lemon juice and a drizzle of remaining olive oil, if desired.