Make the Dressing:
Add mustard, balsamic vinegar, and olive oil to a narrow jar. Season with salt and pepper.
Blend with an immersion blender for about 10 seconds until creamy and emulsified, like a thick mayonnaise.
Refrigerate until ready to use.
The dressing keeps well for weeks in the fridge.
Cook the Lentils:
Rinse the lentils and cook in a pot of salted water (or vegetable broth) for about 20 minutes over medium heat, or according to package directions.
Drain well and let cool slightly.
Prep the Cabbage:
Remove the tough inner core from both cabbages and slice finely.
Add to a large bowl, drizzle with olive oil and a pinch of salt, and massage for 1 minute to soften.
Assemble the Salad:
Add rucola and chopped sun-dried tomatoes to the bowl.
Mix in the cooked lentils and drizzle with the creamy balsamic dressing. Toss gently to combine.
Taste and adjust seasoning.
Serve & Enjoy:
Serve immediately, or chill for 30 minutes to let the flavors develop.
Optional: Top with a generous spoonful of beetroot hummus for a creamy contrast.