Place diced potatoes in a microwave safe bowl and add water. Cover and microwave for 5 minutes.
While potatoes are in the microwave, Combine sauce ingredients and set aside.
In a large hot skillet, add butter, turn heat down to medium high, and melt until hot and bubbly, being careful not to burn. Add onion, kielbasa, and pepper and cook for 2-3 minutes until onion is translucent and kielbasa begins to brown. Remove potatoes from microwave and drain any remaining water. Add potatoes to the skillet and cook until potatoes are completely cooked through, about 10 more minutes. Add sauce to potato mixture and toss to coat evenly. Add spinach, cover skillet with a lid and let simmer for 2 minutes, until spinach has wilted, tossing once or twice during the cooking time. Serve.
I highly recommend using a large skillet. When you add the spinach, you are going to need the room.
Nutrition information calculated using myfitnesspal is provided as a courtesy, but will vary depending on the specific brands of ingredients you use. Please consult with your doctor regarding specific health needs.