Preheat the grill to medium heat. Cut the Thomas’ English Muffins in half. Then whisk the milk, eggs, sugar, and salt together in a medium bowl. Set aside. Place a large cast iron skillet on one side of the grill for the Bananas Foster.
Dunk the English Muffins halves, 2-3 at a time, in the egg mixture. Stand back for safety and spray the hot grates with nonstick cooking spray. Grill the French toast cut side up. Once the egg mixture absorbs, spoon a little extra over the top of each piece. Grill for 2-4 minutes, then flip and grill another 2-4 minutes. Repeat with the remaining English Muffin halves. Re-spray grates each time.
Meanwhile, place the butter in the hot skillet. Once melted add the rum and banana liqueur. Stand back and let the alcohol burn off the skillet. Once the flame subsides, add the brown sugar, apple pie spice, and salt. Stir until the sauce simmers, then add the bananas. Gently stir and let the bananas simmer for 2-3 minutes and remove from heat.
Serve the Grilled French Toast warm with hot Bananas Foster scooped over the top.