Cook 10 oz dry pasta according to the instructions on the package.
While the pasta is cooking, cut 9 oz tempeh into approximately 1-inch pieces.
Bring a pot of water to a boil, add the tempeh pieces, then reduce to a simmer.
Cook the tempeh for 15 minutes, adjusting the heat as needed to maintain a simmer.
Drain and discard the cooking water, then add the tempeh pieces to a blender, along with 1 cup water (fresh water—not the cooking water), 1/3 cup nutritional yeast, 1/4 cup extra virgin olive oil, zest of 1 medium lemon, 2 tablespoons fresh lemon juice, 3/4 teaspoon salt, and 1/2 of 1 small garlic clove.
Blend until smooth and creamy.
Transfer the sauce to a pot on the stove set to medium heat, add the cooked pasta, then cook, stirring frequently until hot (you can reuse the same pot you cooked the pasta in).
Garnish with capers, black pepper, and finely chopped chives before serving, if desired.