Cook pasta according to package directions. Drain well.
Meanwhile in a large skillet, heat 1 tsp olive oil over medium heat. Squeeze sausage out of casing directly into skillet, breaking up any large pieces with spoon. Cook until brown. Transfer to plate.
Add remaining 1 tsp to skillet. Cook onions and garlic for about 3 minutes.
Stir in tomatoes, oregano, pepper, and sausage. Increase heat to bring to simmer. Reduce heat and allowed to simmer uncovered for about 5 minutes. Add spinach and only cook until spinach is slightly wilted. Remove from heat.
Add pasta to sausage mixture and stir well. After dishing up appropriate serving size to plate, sprinkle with feta cheese and additional oregano, if desired. Serve and enjoy!