Preheat the oven to 450°.
Rinse the lentils. Pick out any small stones or bad lentils.
Heat a large, non-stick saute pan over medium heat (I use a non-teflon Scan Pan).
Add the bacon and cook over moderate heat until golden brown, about 4 minutes.
Add the onion and cook, stirring, for 3 minutes.
Add the stock, whole garlic cloves, carrot, leek, bell pepper, zucchini, lentils and thyme plus 1/2 cup water and bring to a simmer. Simmer over low heat for 25-30 minutes. Lentils should be tender when cooked.
Coat a baking dish with non-stick cooking spray and arrange the chicken. Season well with salt and pepper. Roast on the top rack for about 40 minutes, until cooked through.
Discard the thyme sprig from the lentils.
Transfer the garlic, carrot, leek and bell pepper to a blender. Add 1/4 cup of the cooking liquid and puree.
Drain the lentils and return them to the pot. Stir in the pureed vegetables.
In a small skillet, heat the tablespoon of olive oil. Add the chopped garlic and cook over low heat for 1 minute.
Add 1 teaspoon of pimentón. Scrape the mixture into the lentils and simmer for 5 minutes.
Add the spinach and vinegar, stirring until the spinach is just wilted and season with salt to taste. Serve the lentils in bowls topped with the chicken.