Vertically cut each bell pepper in half. Remove the stems and membrane and scoop out the seeds. Drizzle olive oil on a cookie sheet lined with parchment paper and place the peppers flesh-side up. Give the peppers a little drizzle of olive oil and a good sprinkle of salt and pepper.
In a medium bowl, add both cheeses. Place 1/2 of the cheese over all of the halved peppers. Slice the tomatoes into 8 slices and put a slice in the cavity of each pepper. Cover each pepper with remaining cheddar cheese. Bake peppers until the peppers are almost done, about 30 minutes.
Meanwhile, in a skillet, drizzle olive oil and brown the ground sausage over medium-high heat until just browned, about 8 minutes.
When peppers are almost soft, remove them from the oven and divide the sausage among the peppers. Sprinkle the Parmesan cheese over the sausage and bake for about 8 to 10 minutes more, or until the cheese is slightly brown.
Remove from oven, add red pepper flakes or hot sauce and a dollop of sour cream if you desire and serve immediately.