Heat the olive oil in a large saucepan over medium-high heat. Add the pancetta and render the fat; cook until the edges are crispy, about 5 minutes. Add the onion, carrots and celery and saute until tender, about 6 minutes. Toss in the garlic and saute until fragrant, about 1 minute. Add the lentils and cover with water by 2 inches. Bring to a boil, reduce the heat to a low simmer and cook until the lentils are tender but not falling apart, about 18 minutes. Drain well and let cool.
Put the mixed greens in a large bowl. Add the lentils, burrata and a sprinkle of, olive oil and mix to combine.