Saute prosciutto and onions in a frying pan in the extra-virgin olive oil, rosemary and hot peppers on high heat, until the prosciutto and onions are browned.
Add the lentils to the pan. Cook for a few minutes so that the lentils absorb the flavors of the other ingredients. Add a pinch of salt, but be cautioned that the prosciutto is already quite salty.
Remove the rosemary sprig and plate the lentils. Serve warm or at room temperature.