In a dry large frying pan over medium heat, toast the nigella seeds, stirring often, until fragrant, 3 to 4 minutes. Transfer to a plate to cool.

• Pat the steaks dry with a paper towel; season generously with salt and pepper.

For the top sirloins and filet mignons:
In the same pan used for the nigella seeds, warm 1 to 2 tablespoons oil over medium-high heat until hot but not smoking. Add the steaks and cook, turning frequently, until well browned, 6 to 8 minutes for medium-rare for top sirloins and 8 to 12 minutes for filet mignons. Transfer to a plate to rest for 5 minutes.

For the rib-eyes:
In the same pan used for the nigella seeds, warm 1 to 2 tablespoons oil over medium-high heat until hot but not smoking. Add the steaks and cook, turning once, until well browned, 1 to 2 minutes per side for medium-rare. Transfer to a plate to rest for 5 minutes.

While the steaks cook and rest, prepare the cucumber-radish salad.

• Zest and juice the lemon, keeping the zest and juice separate.
• Peel the cucumber, if desired; cut the cucumber in half lengthwise, then on the diagonal into enough thin slices to measure 3 cups [6 cups].
• Thinly slice the celery on the diagonal.
• Cut the radishes in half, then cut the halves into thin half-moons.
• Coarsely chop the walnuts.
• Strip the parsley leaves from the stems; coarsely chop the leaves.

In a large bowl, stir together the lemon zest, 1 tablespoon [2 TBL] lemon juice, and 1 to 2 tablespoons oil; season to taste with salt and pepper. Add the cucumber, celery, radishes, walnuts, parsley, and nigella seeds and toss to coat. Season to taste with salt and pepper.

Spoon 1 tablespoon arugula pesto onto each individual plate and top with the steaks. Serve the cucumber-radish salad and remaining pesto on the side.