Cook spaghetti in a pot of boiling salted water until al dente, about 7 minutes. Reserve 1 cup pasta cooking water and drain pasta.
Heat olive oil in a small skillet over medium heat until it shimmers, then cook garlic, stirring, until golden, about 3 minutes. Transfer garlic with a slotted spoon to paper towels to drain.
In a large skillet, heat 1 tablespoon of the oil from the sun dried tomatoes. Add sun dried tomatoes, spinach, and balsamic vinegar. Cook over medium-high heat until spinach is wilted, about 3-4 minutes.
Toss spaghetti with the sun dried tomatoes and spinach. Stir in the 1/2 cup pasta water. Season with salt and pepper. Sprinkle spaghetti with feta cheese and toasted garlic chips. Serve warm.