Whoa, okay weight gain will happen when you eat more calories than you consume. The "usual" guidelines you'll see tossed around for protein and fat are to ensure at least a gram of protein per pound lean mass, and at least half a gram of fat per pound lean mass. Higher is fine, just don't go lower.
"Lean gainer" LMAO! It all comes down to calories and partitioning. If you eat more calories than you need, you gain. Do this while you lift weights regularly, and you gain some muscle. Eat too much more than you need, you'll gain too much fat while you add muscle - adjust your calories accordingly.