Preheat the oven to 375°F. Place a rack in the lower and middle thirds of the oven.
Line a sheet pan with parchment paper and carefully lay the slices of prosciutto in a single layer.
In an 8”x8” baking pan, add the cherry tomatoes in a single layer along with the olive oil, Italian seasoning and a good pinch each of salt and pepper. Give the pan a good shake to fully coat.
Place the prosciutto on the bottom rack and tomatoes on the top rack of the oven and bake for 10 minutes.
Remove the prosciutto from the oven, flip the pieces, return to the oven and give the tomato pan a shake. Bake for another 5 minutes until the prosciutto is crispy.
Remove the prosciutto and let cool. Continue baking the tomatoes for another 10-15 minutes until they soften and collapse a little bit. Remove from the oven and let cool completely.
In a large pot of boiling salted water, cook the tortellini 4 minutes. Drain and rinse with cold water. Turn out onto a layer of paper towels and blot dry.
For the dressing, drain off and measure the oil from the tomatoes; you should have around 2 tablespoons. Top off with fresh olive oil to reach ¼ cup and pour it into a large jar with a tight fitting lid. Add the remining dressing ingredients, screw on the lid and shake very well until combined. Can be made several days in advance and refrigerated.
In a large bowl, add tortellini, lettuce and red onion. Pour about 1/3 of the dressing on top and toss until evenly coated, using more as needed.
Crumble the crispy prosciutto on top, add the shaved parmesan and roasted tomatoes and toss gently to combine. Drizzle more dressing on top if desired.
Packaged prosciutto usually comes with heavy waxed paper between the slices. Carefully separate the slices, leaving that paper intact on one side. Lay the prosciutto meat side down on the parchment lined pan and carefully pull back the sheet of waxed paper. This method is much easier than trying to arrange a flexible piece of thinly sliced meat evenly on the sheet pan.
The roasted tomatoes are very soft; gently toss once added to avoid too much breakage.
If you like, add diced avocado to the salad at the very end.