Heat a skillet over medium-high heat with a splash of olive oil. Season the beef with salt, pepper, and oregano. Cook until nicely browned and just cooked through, breaking it up as you go.
Meanwhile, toss cherry tomatoes, cucumber, and red onion with a pinch of salt. If you’re feeling fancy, squeeze a tiny bit of lemon over them to wake up the flavors.
Warm the grains (if using) per package instructions. Fluff them and drizzle a little olive oil for shine.
Assemble: lay a bed of greens in each bowl, top with grains, then the cooked beef, and a generous scoop of tzatziki. Scatter tomatoes, cucumber, red onion, and feta over the top.
Squeeze a touch more lemon if you like a bright finish, and tuck in a few extra herbs if you’ve got them. Serve immediately and pretend you planned this all along.