Place the rosemary, garlic, oregano, 1 tablespoon salt, and 1 1/2 teaspoons pepper in a food processor and process until minced. Add the olive oil and process into a coarse paste. Place the lamb on a sheet pan with the rib ends pointing down and spread the paste evenly on top of both racks. Cover and refrigerate for at least 6 hours.
When ready to cook, preheat the oven to 450 degrees F.
Roast the lamb for 25 minutes exactly for medium rare and 30 minutes for medium. Remove from the oven and cover the pan tightly with aluminum foil. Allow the lamb to rest for 15 minutes. The internal temperature should read about 140 degrees when an instant-read thermometer is inserted sideways into the center of the lamb. Slice between the ribs into individual chops and serve hot or warm with Easy Tzatziki.
Grate the cucumber by hand on a box grater, as you would grate carrots. Squeeze the cucumber with your hands to remove a lot (but not all) of the liquid. Place in a medium bowl and stir in the yogurt, sour cream, lemon juice, vinegar, dill, garlic, 2 teaspoons salt, and 1/2 teaspoon pepper. Serve cold or at room temperature.