Preheat oven to 400 F.
Cut watermelon into 6 equal sized pieces. About ½-inch thick.
Remove rind and seeds (if there are seeds).
Use a baking sheet and line with aluminum foil.
Lightly grease foil with avocado oil.
Place watermelon pieces on baking sheet. Don't allow them to touch.
Season with salt, pepper and a touch of vinegar.
Cover melon steaks with a sheet of foil.
Cook for 28-30 minutes.
Remove melon from oven and remove top foil sheet.
Top steaks with pistachio.
You may want to add a bit more seasoning depending on taste.
Return to oven.
Cook for 10-12 minutes.
When serving, spoon juices over each steak.
Eat warm.