Cook the whole-grain penne in a large pot of salted boiling water according to package directions until al dente; drain and set aside.
Heat 1 tablespoon of the olive oil in a large skillet over medium-low heat. Add the minced garlic and cook, stirring, until fragrant, about 1 minute.
Add the chopped sun-dried tomatoes, black pepper, salt to taste, and crushed red pepper flakes to the skillet and sauté until the tomatoes soften, about 5 minutes.
Toss the cooked penne with the remaining 1 tablespoon olive oil in the skillet; stir to coat, cover, and cook on low for 2 minutes.
Add the pine nuts and baby spinach to the pasta, tossing until the spinach begins to wilt.
Remove the skillet from the heat, cover, and let the spinach slightly wilt for about 2 minutes.
Sprinkle the feta cheese over the pasta, toss gently, and serve.