Place The Beef Tongue In A Slow Cooker And Cover With Water. Add The Onion Slices, Garlic, And Bay Leaf. Season With Salt. Cover And Cook On Low Overnight Or 8 Hours. Remove The Tongue And Shred The Meat Into Strands. Heat The Oil In A Skillet Over Medium Heat. Cook The Tomatoes And Peppers In The Hot Oil Until Softened On All Sides. Remove The Tomatoes And Peppers In A Blender, Keeping The Oil On The Heat; Season With Salt. Blend Briefly Until Still Slightly Chunky. Cook The Diced Onion In The Skillet Until Translucent; Stir In The Tomato Mixture. Cook Another 5 To 6 Minutes. Build The Tacos By Placing Shredded Tongue Meat Into A Tortilla And Spooning Salsa Over The Meat.