How to Make It
In a shallow nonreactive baking dish, combine all the ingredients except the venison. Add the venison and turn to coat. Cover and refrigerate for at least 8 hours or overnight.
Heat the oil in a nonreactive saucepan. Add the onion and carrot and cook over moderately high heat, stirring, until the onion is softened. Stir in the garlic and cumin and cook for 2 minutes. Add the lentils, chicken stock and thyme and bring to a simmer. Cover and simmer over low heat, stirring, until tender, about 40 minutes. Stir in the vinegar and season with salt and pepper. Reserve 1/4 cup of the cooking liquid. Cover the lentils and keep warm.
Heat 1 teaspoon of the olive oil in a large nonreactive skillet. Add the spinach by handfuls and stir over high heat until wilted before adding more. Transfer to a bowl, discarding any liquid.
Heat 1 tablespoon plus 2 teaspoons of the olive oil in the skillet. Add the shallots and cook, stirring, until lightly browned. Add the sage and vinegar. Stir in the spinach. Add the reserved lentil cooking liquid and season with salt and pepper. Return to the bowl and keep warm.
Pat the venison dry with paper towels and cut the meat into 24 medallions; they should be about 3/4 inch thick for tenderloin and 1/2 inch thick for loin. Season with salt and pepper. Heat 1 tablespoon of the remaining oil in each of 2 large skillets until smoking. Add the medallions and sear over high heat, turning once, until well browned but still rare inside, 3 to 5 minutes.
Drain the lentils and mound them on 8 plates. Arrange the venison medallions over the lentils, top with the spinach salad and serve at once.