I make this vinaigrette all the time. I think most people tend to do the balsamic and olive oil, but the tanginess of the Dijon and the freshness of the lemon juice is really unparalleled. Shallots are also just nice on anything. This is a v versatile dressing: you can carry any herbs you're using in your main course to this dressing. Thyme is especially nice! This dressing on arugula is a quick meal. I also love this dressing because the acidic lemon gives salty flavor and adding extra salt is not necessary! I really like not cooking with salt. That's one of the main reasons I can't eat at restaurants frequently... the salt makes me thirst all day long!
1 tsp lemon juice
1 tsp Dijon mustard (please don't cheap out on this ingredien)
1 tsp herbs (thyme, oregano, parsley, etc etc)
1 tsp grated shallot
1/4 tsp garlic powder
1 TBSP olive oil
Whisk everything together and enjoy. You can do just the lemon, mustard and oil if that's all you have. You can add anything you want to this.