Slice calamari tubes into rings and pat everything very dry.
Heat a flat-top or cast-iron skillet until extremely hot.
Add a little oil and sear calamari 45–60 seconds undisturbed for char.
Toss quickly and cook 1–2 minutes total until just opaque; remove at once.
In another pan, sauté garlic in oil, then wilt the spinach briefly.
Combine diced tomatoes, remaining garlic, parsley, salt, and pepper.
Grill lemon halves cut-side down until lightly charred.
Plate spinach, top with calamari and tomato mixture, add grilled lemon and extra parsley.