Roast the poblano pepper: preheat the broiler then put poblano-pepper onto the oven rack about 4 inch from broiler element. Cook till blackened on the top and then flip over. Broil till blackened.
Continue rotating & broiling till blackened till all sides are blistered. Alternately, carefully hold the pepper using heat-proof tongs into a gas stove fire (or put on top of stove stand), rotating to blacken all of the sides. Set aside and let cool slightly.
Make the smoky sauce: if poblano pepper is cooled to the touch, then peel off the blackened skin then remove seeds and stem. Blend all ingredients in a food-processor & mix till very-smooth.
In a large-skillet over moderate heat, brown ground-beef, breaking-up with a spatulate. Add in mushrooms and saute till softened and liquid is evaporated just a couple of minutes.
Stir in poblano-salsa-sauce & reduce heat . Cook a few minutes till bubbly and a little thickened. Remove from heat.
Make the cilantro lime cauliflower-rice: stir together steamed cauliflower-rice, juice of 1 lime, roughly ⅓ - ½ cup cilantro and salt.
Make fast guacamole: Mash together avocado-meat, ½ cup red onion, juice of 1 lime, ½ - ⅔ cup cilantro and salt.
Serve your Whole30 chipotle steak and avocado bowls: divide cilantro lime cauliflower-rice among of bowls, then top with beef mixture.
Finish with a few large, heaping spoonfuls of guacamole. Garnish with additional red onion and chopped cilantro, if desired.