In a 3 qt. sauce pan, over medium high heat, bring salted water to a boil and cook lentils to al denté, stirring occasionally, approximately 15 minutes. Strain, cool with cold water to halt the cooking, and set aside.

In a sauté pan over medium heat, add the butter, salt, onions, carrots, and celery. Sweat until onions are translucent, about 4-6 minutes. Add garlic and continue until fragrant, stirring and being careful not to burn the garlic, additional 2-3 minutes. Add capers and combine until just warmed through.

Reduce heat to low. Add reserved lentils to the sauté pan and mix until warmed through.

Season with lemon juice and serve immediately.