Preheat the oven to 425F convection. Line a baking sheet with parchment paper.
To the baking sheet, add mushrooms and potatoes. Drizzle the oil, salt, and pepper all over and use your hands to toss to coat well. Spread into an even layer. Nestle the sausages into the veggies.
Bake for 25-30 minutes or until potatoes are crisping up a bit (you can remove the sausages as soon as they start to get some color, about 15-20 minutes).
Make four spaces on the sheet pan and crack the eggs into them. Sprinkle the eggs with a little bit of salt. Bake for another 5-8 minutes, depending on how done you want the eggs (they’ll continue to cook a bit as they cool off).
Meanwhile, pan-fry the tomatoes (if using) in about 1 tablespoon of butter or oil over medium-high heat for about 2-3 minutes per side.
Add everything to your plate (veg, sausage, egg, tomato) along with any additional items (cheddar, toast, baked beans, herbs).