Peeled and cut the watermelon and avocado into 1 ½ inch cubes.
Open the lid of the Instant Indoor Grill and place inside of the basket the Grill plate.
Select the Grill function, press Temp and select L5, press Time and set the time to 3 Minutes. Press Start.
Once the grill finishes preheating and displays Add Food, place watermelon, avocado, and red onion inside of the basket, press down on the vegetables, grill in batches if needed.
In the meantime, in a small bowl mix all the dressing ingredients until well combined. Set aside.
When the unit displays Turn Food open the lid and flip all the vegetables, press down again, close the lid.
Once the cooking time has finished transfer them to a cutting board and allow them to cool down.
Once cool, transfer the grilled vegetables to a bowl and add in the diced cucumber, baby spinach, feta cheese and basil, pour the dressing over the salad, adjust the seasoning with salt and pepper if needed.