Preheat the oven to fan 170C/ conventional 190C/gas 5. Melt the butter in a medium saucepan and cook the green vegetables and onions for 5 minutes, stirring until starting to soften. Tip the milk and flour into the pan and stir over the heat until it thickens to a smooth sauce. Cool for 5 minutes or so, stirring to stop a skin forming.
Beat the eggs into the sauce and generously season. Pour into the pastry case and scatter with the goat's cheese and tomatoes.
Bake for 40 minutes until the filling is set, turning golden. Cool for a few minutes before taking from the tin. Serve with a green salad.