Toss together lamb, olive oil, vinegar, garlic, cumin, salt and pepper. Let stand for 30 to 60 minutes.
Meanwhile, in a blender, purée cilantro and 1/4 cup water until smooth; set aside.
Strain lamb, reserving marinade. In a large bowl, toss lamb with flour, shaking off excess. Heat oil in Dutch oven or large saucepan set over high heat. Cook lamb, in two batches, for 3 to 4 minutes per side or until starting to brown all over. Transfer to a plate.
In the same skillet, cook onion and aji peppers over medium heat for 3 to 5 minutes or until tender and fragrant. Stir in beer and chicken broth; bring to boil. Return lamb to pan. Reduce heat to medium-low; stir in cilantro purée. Cover and cook for 1 hour. Stir in potatoes and carrots; cover and cook for 40 to 45 minutes or until lamb and vegetables are very tender and sauce is thickened.
Meanwhile, whisk together 1/2 cup chicken broth with achiote paste until smooth. In a large saucepan, combine remaining chicken broth, achiote mixture, garlic, salt and pepper; bring to boil. Stir in rice and beans. Reduce heat to low; cover and cook for 20 to 25 minutes or until rice is tender and most of the liquid is absorbed. Remove from heat. Let stand, covered, for 10 minutes; fluff with a fork before serving.
Toss together red onions, yellow pepper, jalapeño, cilantro, lime juice, oil, vinegar and salt. Let stand for 10 to 15 minutes or until onions are lightly pickled.
Serve stew with rice and beans, and onion salad.
Aji chili peppers are also known as Peruvian hot peppers. They have a fruity flavor and range in heat. If unavailable, substitute aji amarillo paste or your favorite fresh chili pepper. Scotch bonnet, habanero or serrano are all good substitutes.