Preheat the oven to 180 ºC or 350 ºF. Dice the sweet potato and transfer to a baking dish or tray. Sprinkle with olive oil, salt and pepper. Roast for 20 minutes.
Put the grains in a large pot or skillet and pour the vegetable broth in it. Bring to a boil and lower the heat.
Meanwhile, finely chop garlic, chop onion, peel and slice carrots and leek. Heat a lug of olive oil in a saucepan or skillet. Add vegetables in it and stir-fry for about 5 minutes. Transfer to the broth. Add diced tomatoes with juice, drained beans, bay leaves, smoked and sweet paprika. Simmer for 30 minutes.
Once the sweet potatoes are ready, add them to the stew together with olives. Before the end, add ground hazelnuts and season with salt and black pepper.
Make the bread crumbs: heat a lug of olive oil in the skillet you used for onions over medium-high heat. Break bread slices with your fingers into small pieces and transfer them to the skillet. Add garlic powder, salt and black pepper and fry until golden and crispy, about 4 minutes, stirring occasionally.
Serve the stew with breadcrumbs, ground hazelnuts, fresh herbs and (optional) sour cream. Enjoy!