1. Preheat your oven to 375 degrees Fahrenheit (190 Celsius)
2. If you have not already done so, peel and slice your onions, remove the seeds from your bell peppers and slice, core and slice your apple, and remove the seeds from your jalapeno and then slice it
3. Place your onions, peppers, apples, and jalapenos in a 12 inch cast iron skillet or large pyrex baking dish
4. Add your duck fat and lemon juice and mix well ensuring an even coating
5. Sprinkle with salt and pepper to your taste liking
6. Take your sausages and place them on your bed of vegetables
7. Using a sharp knife, poke 5-10 holes around each sausage so they don't explode in your oven
8. If you have a leave in meat thermometer, now is the time to insert it into one of your sausages
9. Cover your pan or dish with aluminum foil and place in your preheated oven
10. After 25 minutes remove the aluminum foil to allow the sausages to brown until they are finished
11. I used a meat thermometer and mine took 35 minutes to finish to an internal temperature of 165 degrees Fahrenheit (73 Celsius)
12. Remove from the oven when done and sprinkle with dried or fresh thyme and serve

Notes