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 to the skillet and sauté until fragrant, about 1 minute.
Add the chopped sun-dried tomatoes, black pepper, salt, and crushed red pepper flakes; continue to sauté 4–5 minutes until the tomatoes soften.
Add the cooked penne and the remaining 1 tablespoon olive oil to the skillet; toss to coat, cover, and cook on low for 2 minutes.
Add the pine nuts and baby spinach and toss until combined; turn off the heat, cover, and allow the spinach to wilt slightly, about 2 minutes.
Sprinkle the feta cheese over the pasta, toss gently to distribute, and serve.