Preheat the oven to 218°C. Heat the oil in a medium frying pan over medium-high heat. Add the chopped garlic, carrots and onions and cook until tender and beginning to brown, 5 minutes. Add the turkey and thyme and continue to cook, breaking up with a spoon, until the turkey is cooked through and lightly browned. Stir in the ketchup and cook until lightly caramelised. Stir the broth and flour together in a small bowl until smooth and then pour into the pan. Cook, until thickened, 2 minutes. Stir in the peas and season with 1/4 teaspoon salt. Remove from the heat and divide among four ramekins.
Meanwhile, place the potatoes in a medium pot and cover with cold salted water. Bring to a boil and continue to cook until tender when pierced with a knife. Drain the potatoes and return to the pot over low heat. Add the milk, cheese and spring onions and mash until smooth. Season with salt and pepper.
Transfer the filled ramekins to a rimmed baking sheet and evenly top with the mashed potatoes. Lightly mist with nonstick cooking spray and bake until the potatoes are lightly browned and the turkey filling is bubbly around the edges, 15 minutes.