Heat the oil in a large, heavy-based saucepan and cook the onion and bacon over a medium heat, stirring frequently, for 5 minutes until the onion is softened and the bacon browned. Add the mint and potatoes and cook, stirring, for 1 minute, then add the peas and stock. Bring to the boil, then reduce the heat, cover and simmer for 15 minutes until the potatoes are tender.
Transfer the soup in 2 batches to a food processor and whizz until smooth. Return to the pan, swirl in the crème fraîche and heat through for 1 minute.
Season with a little salt and pepper, then ladle into warmed serving bowls and scatter with roasted seeds to serve.