Heat the olive oil in a large pot over medium heat. Add the onion and cook for 5 minutes until it softens.
Stir in the garlic, cumin, paprika, and red pepper flakes. Cook for 1 minute until the spices smell fragrant.
Add the diced tomatoes with their juices and cook for 2 minutes, stirring to combine.
Pour in the vegetable broth and add the red lentils. Bring the mixture to a boil, then reduce the heat to low and simmer for 15 minutes.
Stir in the bulgur and salt. Continue simmering for 10 more minutes until the lentils and bulgur are tender and the stew has thickened.
Remove the pot from the heat. Ladle the stew into bowls and top each serving with the chopped fresh mint.