Prepare a grill fire to 375°.
Scrub and peel potatoes. Slice thin, a mandoline makes it easy to get uniform slices.
Rinse the potatoes well to remove the extra starch and pat dry.
Toss potatoes with olive oil, salt and pepper.
Place in a single layer on a rimmed sheet pan.
Cook on the grill with the lid closed about 20- 30 minutes or until potatoes are softened and cooked through.
Remove from grill.
Cover the bottom of a 10 inch skillet with potato slices.
Top with a layer of smoked brisket.
Sprinkle with a layer of colby jack cheese.
Add another layer of potatoes.
Top with a combination of colby jack and mozzarella cheese.
Add a layer of sliced onions and diced tomatoes.
Return to the grill and cook another 15- 20 minutes until cheese is melted.
Remove from grill and garnish with jalapeños and cilantro.
Slice and serve immediately.