Preheat oven to 400 degrees. Whisk eggs and Dijon together in a small bowl and set aside.
In a non stick, oven safe skillet, melt butter. Add the onion and sugar. Let them soften while occasionally stirring for about 7 minutes. Remove to a plate.
Add bacon to pan and fry on medium high heat until crisp. Remove to the plate with the onions. Pour off about 1 Tbsp. of fat. Once bacon is cooled, crumble into bite size pieces.
Reduce heat to medium and add mushrooms and sage to pan. Cook for 5 minutes while stirring occasionally, then add onions and bacon back to pan.
Add egg mixture and top with cheese. Let it set for 5 minutes and then put in the oven to bake for 10 minutes.
Remove from the oven and let it stand for 2 minutes before serving.