To cook the fajita-style veggies, heat a large pan over medium high heat with a drizzle of oil.
Add the vegetables and sprinkle over the fajita seasoning. Cook the veggies, tossing them occasionally, until they have softened and start to charr a little on the edges. Remove from heat and set aside.
To assemble the grilled cheese, butter the slices of bread on one side. Place 2 slices into a large pan, over medium heat, butter side down.
Place 2 slices of Dubliner Mature White onto each slice of bread, then top with the grilled fajita-style veggies. Drizzle over a bit of habanero sauce, if using, then lay another 2 slices of cheese onto each.
Finally, place the remaining 2 slices of bread on top, buttered side up.
Grill until golden underneath, about 4 minutes, then carefully flip sandwiches over and toast for another 4 minutes so that the underside is golden and the cheese has melted.
Remove from the pan, cut sandwiches in halves, and enjoy.