Preheat oven to 180°C and grease a 12-hole medium or large muffin tin with olive oil/butter. Bring a half kettle of water to the boil.
Heat olive oil/butter in a small fry-pan on medium heat. Cook spring onion, thyme/rosemary and bacon (if using) for a few minutes. Place spinach in a heatproof bowl and pour over boiling water to cover. Leave for about 2 minutes then drain well, squeeze out as much excess water as you can, and finely chop.
In a large bowl, whisk eggs with yoghurt, spinach, spring onion mixture and salt until well combined. Pour into a jug (this will make it much easier to pour into muffin tins).
Divide mixture equally between muffin tin holes, being careful not to overfill - it should come up no more than three-quarters of the way. Top each with some pumpkin, smoked salmon (if using instead of bacon), and a cherry tomato half. Crumble feta on top and sprinkle with reserved green spring onion. Grind over black pepper. Bake for 18-20 minutes until egg is set. Allow to cool in the tin for a few minutes before using a knife to cut around and separate from the edges of the muffin tin and life them out.
Serve warm (see tip) or cold with a side salad and, if you like, a teaspoon of tomato chutney on the side. If not eating immediately, allow to cool before storing in an airtight container in the fridge where they'll keep for up to 3 days.