Preheat oven to 200oC (400oF) and line a large baking tray (or 2 medium sized trays) with either parchment/baking paper or a silicone baking mat.
Peel and deseed the butternut pumpkin (squash) and dice into 1-2inch cubes.
Peel and quarter the red onions and toss in a bowl with the pumpkin, oil and torn up sage leaves. Season with salt and pepper and spread evenly over the baking tray(s).
Bake for 40minutes or until the pumpkin and onions are soft and golden. Once cooked, leave to cool approx. 15minutes before continuing with the salad assembly.
Drain and rinse the lentils and place in a serving bowl. Add the torn tarragon leaves and use your hands to crush/crumble the feta into the bowl as well.
Combine the lemon juice and crushed clove of garlic with a pinch of salt and pepper. Mix this lemon dressing, the slightly cooled pumpkin and onions and the lentil/cheese mixture well before serving.