Finely dice or use a food processor to pulse the bell pepper and jalapeño until finely diced. Use a paper towel to squeeze out excess liquid.
Add the peppers, sugar, apple cider vinegar and salt to a medium pot and bring to a boil over medium high heat.
Continue to boil, stirring occasionally until the mixture begins to thicken, about 10 minutes (the temperature should read 220ºF / 104ºC).
Remove from heat and pour into a clean jar. Let the jelly come to room temperature, then seal and refrigerate until ready to use.
Thinly spread one side of each bread slice with the mayonnaise. Heat a large skillet or griddle over medium-low heat, add the butter and allow to melt.
Place half of the slices of bread, mayo-side down, on the pan or griddle. Divide the cheese evenly on top of the bread slices.
Top each with 3 tablespoons (55g) of the pepper jelly, slices of bacon and spread apple slices over the jelly. Top each with a second slice of bread, mayonnaise side up.
When the underside is golden, about 3 minutes, use a spatula to flip the grilled cheese and continue to cook until the cheese has melted, about an additional 3 minutes.
Remove to a cutting board and cut each sandwich in half. Serve immediately.