Preheat the slow cooker if necessary; see the manufacturer's instructions. Grease 4 heatproof dishes, each 150 ml (5 fl oz), with a little of the butter, checking first they will fit in the slow cooker pot, then press a slice of ham into each to line the base and sides, leaving a small overhang of ham above the dish.
Add 1 teaspoon of chutney to the base of each dish, then break an egg on top. Add a cherry tomato half to each, sprinkle with the spring onion and a little salt and pepper, then dot with the remaining butter.
Cover each one with a square of foil and put the dishes into the slow cooker pot. Pour boiling water into the pot to come halfway up the sides of the dishes. Cover with the lid and cook on high for 40–50 minutes or until the egg whites are set and the yolks still slightly soft.
Lift the dishes out of the slow cooker pot using a tea towel and remove the foil. Loosen between the ham and the edge of the dishes with a knife and turn out. Quickly turn the baked eggs the right way up and arrange each one on a plate with hot buttered toast fingers.