Shred the onion, carrot, and jalapeno pepper using a grater or food processor (I find that this gives me a better texture than dicing; it's important to get the veggies chopped very fine but but not puréed).
Pour 1/4 cup oil into a saucepan on medium heat, then add the shredded veggies. Sauté for around ten minutes or until the onions are lightly caramelized and starting to stick to the pan.
Meanwhile, chop the tomato (400g) and mince the garlic (25g), or pulse together in a food processor.
Add 1–2 tbsp berbere seasoning and 1 tbsp tomato paste to the saucepan and sauté for another minute, then add the chopped tomato and garlic, along with salt and black pepper.
Lower the heat to minimum and simmer, uncovered, for 30–45 minutes, stirring occasionally to prevent sticking and burning on the bottom.
When the tomatoes have broken down and the sauce is a nice thick consistency, remove from heat and squeeze in 1 tbsp lemon juice.