Align Samus with the edge of the horizontal platform above the door and run towards the open door. After taking approximately two steps forward, jump and hold jump. After the transition, hold down. With proper timing, you should have entered the lava pool without losing any momentum. From there, morph and hold left during the dive until you reach the far left Namihe. Jump on top of the Namihe, making sure to avoid any fireballs in the way. Walljump off of the Namihe above and let your momentum carry you to the right wall below the final Namihe. Walljump in place until an opportune time (when there isn't a fireball in the way) to walljump off of the final Namihe. Alternatively, you can skip walljumping off the final Namihe if you are comfortable doing so. Use your momentum to hit the final walljump off of the side of the top left platform near Ridley's maw.