Heat The Oil In A Large Skillet Or Dutch Oven Over Medium Heat. Add The Onion And Garlic; Cook And Stir Until Fragrant. Add The Cubed Pork, And Cook Until Browned On The Outside. Transfer The Pork, Onions, And Garlic To A Slow Cooker, And Stir In The Green Salsa, Jalapeno Peppers, And Tomatoes. Cover, And Cook On High For 3 Hours. Reduce The Setting To Low, And Cook For 4 To 5 More Hours.