Toast the walnuts in the oven for 3 minutes at 200C/400F, cool and set aside till needed.
Cut the top and the bottom of the grapefruit, so it has two flat ends, then stand it on a cutting board and start removing the peel together with the pith (the white spongy part) with a sharp pairing knife following the natural curve of the fruit. Once no visible white parts remain hold the grapefruit in the palm of your hand and start cutting out little segments of the grapefruit flesh between the membranes. Once you finish segmenting the grapefruit, squeeze out the remaining juice and save it for the dressing.
Alternatively, you can simply peel the grapefruit and slice it if you don’t want to fuss.
Make the salad dressing by combining the Dijon mustard, maple syrup, white wine vinegar, olive oil, a pinch of salt and pepper and the saved earlier grapefruit juice in a mason jar. Cover with a lid and twist it tightly, then shake till well combined and emulsified.
In a large salad bowl combine the salad leaves, grapefruit segments, avocado wedges, crumbled goat cheese and walnuts. Drizzle the dressing all over and mix gently to coat.