Cut pork into strips, and set aside.  

Add oil to a skillet, and heat a over medium heat.  While it heats up, mince shallot. Once hot, add shallot to pan and Sauté for 1 minute, add sliced mushrooms and 1/4 teaspoon salt. Sauté for 2-3 minutes; remove from pan and set aside.

In same skillet add pork and 1 tablespoon of taco seasoning. Stir pork and cook until no longer pink.   Return mushrooms and shallots to the skillet. 

Scoop meat and mushrooms into taco shells, topped with chopped tomatoes and watermelon on the side.