Bring a large pot of salted water to a boil and cook the whole-grain penne until al dente according to package directions; drain and set aside.
Heat 1 tablespoon of the olive oil in a large skillet over medium-low heat.
Add the minced garlic and sauté until fragrant, about 1 minute, taking care not to brown it.
Stir in the chopped sun-dried tomatoes, black pepper, salt to taste, and crushed red pepper flakes; continue to sauté for about 5 minutes until the tomatoes soften.
Add the cooked penne and the remaining 1 tablespoon of olive oil to the skillet; toss to coat, cover, and cook on low for 2 minutes.
Stir in the pine nuts and baby spinach and toss until combined; turn off the heat, cover, and let the residual heat wilt the spinach for about 2 minutes.
Sprinkle the feta cheese over the pasta, toss gently to combine, and serve.