14. STOCK-BASED COMPENSATION (Details Narrative) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				9 Months Ended
	Feb. 28, 2021	Nov. 30, 2020	Aug. 31, 2020	Feb. 29, 2020	Feb. 28, 2021	Feb. 29, 2020
Stock Option and RSU Transactions
Intrinsic value of options exercised	$ 57			$ 92	$ 151	$ 159
Weighted average remaining contractual life of the options exercisable and expected to be exercisable					3 years 8 months 5 days	3 years 9 months 11 days
Restricted stock units granted (in thousands)	4				165
Shares withheld for taxes and not issued (in thousands)	4	0	0		4
Market value on the date of the grant	$ 2.25				$ 1.87
Restricted stock units vested (in thousands)	19			3	34	10
Restricted stock units unvested (in thousands)	143			13	143	13
Restricted stock units unvested intrinsic value	$ 400			$ 27	$ 400	$ 27
Stock Option and RSU Transactions | Board of Directors
Restricted stock units granted (in thousands)	34				126
Market value on the date of the grant	$ 2.25				$ 1.73
2016 Equity Incentive Plan
Stock-based compensation costs capitalized as part of inventory	$ 0			0	$ 0	0
Stock-based compensation expense related to stock options and RSUs	253			166	736	480
Unrecognized stock-based compensation	1,151				$ 1,151
Weighted average period for recognition of costs					2 years 7 months 6 days
Employee Stock Purchase Plan
Weighted average period for recognition of costs					1 year
Stock-based compensation related to the ESPP	18			$ 41	$ 62	$ 131
Compensation cost related to purchase rights under the ESPP but not yet recognized	$ 29				$ 29
ESPP purchase right granted (in thousands)	0			0	81	38
ESPP shares issued (in thousands)					72	71
ESPP shares available for issuance (in thousands)	511			299	511	299