Rinse the quinoa under cold water. Add it to a 2-quart / 1.9 L saucepan with the water (or broth) and 1/4 tsp salt. Bring to a boil, cover, and simmer for 12 to 15 minutes, until the water is absorbed and the quinoa is tender. Fluff with a fork and set aside.
While the quinoa cooks, whisk the dressing: combine 3 tbsp olive oil, lemon juice, lemon zest, garlic, and oregano in a small bowl. Season with salt and pepper, taste, and adjust.
Halve the cherry tomatoes, dice the cucumber, and thinly slice the red onion. Drain and rinse the chickpeas.
Pat the halloumi dry with a paper towel and slice into 6 pieces, about 1 cm thick.
Heat 1 tbsp olive oil in a 10-inch / 25 cm nonstick or cast iron skillet over medium-high heat. Lay the halloumi slices in a single layer, they should not touch.
Sear for 2 to 3 minutes per side, until deep golden brown and slightly crisp at the edges. Flip once with a thin spatula. Halloumi turns rubbery fast if you leave it too long, so watch it closely.
Divide the quinoa among 4 bowls. Top with chickpeas, cherry tomatoes, cucumber, and red onion.
Lay the warm halloumi slices on top of each bowl. Drizzle with the lemon herb dressing and sprinkle with chopped parsley or dill. Serve right away.