Lentil salad with feta, mint and oranges

This started as a way to use up the last of the feta and turned into a new lentil standard. I was surprised by how much the orange and mint brightened the whole thing--those two things took an ordinary lentil salad to the next level. I don't usually spring for fresh mint this time of year ($2 a bunch!) but I was glad I did.

1 cup lentils, cooked in 2 1/2 cups of water until tender (about 25 minutes)
1/4 cup diced red onion or green onion (I left the onion out, so this part is optional)
1/2 cup chopped fresh mint
1 orange, peeled and chopped, with as much of the white part removed as possible
2 big handfuls of crumbled feta

Vinaigrette:
1/4 cup red wine vinegar
1 tablespoon brown or dijon mustard
salt and pepper
1/3 cup olive oil

Combine the first three of the viniagrette, then add the oil in a slow stream while whisking vigorously. Combine the lentils and other things, add the vinaigrette, mix. Serve at room temperature.

This makes a great dish to take to work for lunch, too--because it's best at room temperature, you don't even have to worry about putting it in the work refrigerator.