Roast green beans and lemon slices for 12-15 minutes on a rimmed baking sheet with 1-2 Tbsp of olive oil, salt and pepper. Toss beans once or twice. They should have started to char and brown in spots.
In a small pan heat 2 Tbsp of olive oil. Toast walnuts for 2-4 minutes. Remove from heat, add anchovies and garlic. Stir or swirl pan until anchovies dissolve.
Combine mustard, vinegar, and 2 Tbsp of olive oil in a medium size bowl and season with salt and pepper. Add green beans and toss to coat.
Serve topped with walnuts and chopped dill.
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