Cook pasta al dente as per the instructions given on its packet. Preserve some pasta water, it will be used in the salad dressing.
Put the cooked pasta in a large mixing bowl. Add baby spinach and 1-2 tablespoons of oil from the jar of sundried tomatoes. Gently mix and cover the spinach leaves with hot pasta so they get slightly cooked.
Add sliced onion, cherry tomatoes, sliced sundried tomatoes, olives, chopped walnuts, chopped parsley, or cilantro.
In a grinding jar, put two whole sundried tomatoes, garlic cloves, 2 tablespoons of walnuts, chili flakes, oregano, basil, black pepper, salt, dijon mustard, brown sugar, balsamic vinegar, and 2-3 tablespoons of pasta water preserved in step one. Pulse to make a paste.
Add the paste to the salad bowl.
Also, add around ¼ cup of oil from the jar of sundried tomatoes and add to the salad. Gently toss until everything gets nicely mixed.
Before serving, add feta and more fresh parsley or cilantro.