Prepare the marinade by whisking together the extra-virgin olive oil, fresh lemon juice, garlic powder, salt, and pepper in a small bowl.
Place the drained artichoke hearts and sliced tomato into a resealable plastic bag or a glass jar with a tight-fitting lid.
Pour the prepared marinade over the artichokes and tomatoes. Seal the bag or jar, removing as much air as possible.
Gently toss to ensure everything is evenly coated in the marinade.
Refrigerate for at least 8 hours, or preferably overnight, to allow the flavors to fully develop.
Serve chilled.
Add a pinch of red pepper flakes to the marinade for a gentle, spicy kick.