Cook the barley in water according to package directions.
Add the olive oil to a large skillet or pot over medium heat.
Finely chop the onion and add to the skillet. Turn down the heat if it starts sizzling loudly. The idea is to gently saute the vegetables.
Finely chop the peppers and add to the skillet as you go, stirring occasionally.
Mince the garlic and add to the skillet also.
While the vegetables are cooking, rinse the lentils.
Once the vegetables are tender (about 5 minutes after adding the garlic), add the lentils to the skillet, then the vegetable broth and canned tomatoes. Turn the heat up to high.
Add the paprika, salt, pepper, and red pepper flakes, if using.
Once the liquid is bubbling, turn it down to medium-low and simmer until the lentils are soft, about 25 minutes.
Grate the parmesan cheese if needed.
Remove from heat. Taste and adjust seasonings. Serve over the cooked barley, and top with grated parmesan cheese.