Marinate the meat (thin fillets are best, lamb very finely cut). Bathe it in oil, salt, pepper, and other spices (e.g., cumin, chili, paprika, allspice) as desired, and coat it nicely on all sides.

Cut the bell peppers lengthwise (long green and "normal" red ones)

Throw everything onto the grill/into the pan and fry. If in the pan, use a lid, otherwise the meat will dry out.

Eat.

Homemade mint sauce or tzatziki and (white) bread always go well with this.